The field of art to which this invention is directed is epoxy resin coating compositions.
The basic epoxy resin composition is the diglycidyl ether of a dihydric phenol, the most important of which from a commercial viewpoint is the diglycidyl ether of p,p'-dihydroxydiphenyl propane (Bisphenol A). Such diglycidyl ethers can be converted into thermoset compositions by a wide variety of curing agents, or can be converted into higher molecular weight epoxy resins by reaction with additional dihydric phenol. These higher molecular weight epoxy resins are used primarily in solution coatings wherein they are crosslinked with various crosslinking agents, e.g., aminoplast resins, polyisocyanates or polyamines, or are reacted with unsaturated fatty acids to form epoxy esters.
In addition to modification with dihydric phenols and unsaturated fatty acids, epoxy resins have been modified either by reaction or by blending with a variety of compounds.
Blends of polyglycidyl ethers of polyhydric phenols with epoxidized fatty acid esters, e.g., epoxidized linseed oil, are described in U.S. Pat. No. 2,628,514.
Adhesive compositions made from blends of liquid polyglycidylethers of dihydric phenols, solid polyglycidyl ethers of dihydric phenols and epoxidized fatty acid esters are described in U.S. Pat. No. 2,682,515.
In U.S. Pat. No. 2,944,035, epoxidized fatty acid esters are reacted with mono or polyhydric phenols in such amounts that some of the epoxy groups remain unreacted. The resulting composition is then crosslinked with various crosslinking agents.
U.S. Pat. No. 4,119,640 discloses polymerizable reaction product mixtures made by reacting an epoxidized fatty acid ester with a mixture of acrylic acid, a diepoxide and a modifying compound.
U.S. Pat. No. 4,419,467 describes higher molecular weight epoxy resins made by reacting lower molecular weight epoxy resins with polyether polyols.
In U.S. Pat. No. 4,980,397, higher molecular weight epoxy resins are made by coreacting aliphatic diepoxides, glycidyl ethers of dihydric phenols and dihydric phenols.
Manufacturers of paints and coatings are under increasing government pressure to reduce volatile organic compounds (VOC's) contained in their coating formulations. There is a need for resin systems which can be used to form high solids solutions at viscosities suitable for use in coating formulations.